PT1485747E - Light guide optical device - Google Patents

Abstract

The invention relates to an optical device, comprising a light-transmitting substrate (20) having at least two major surfaces and edges; optical means for coupling light into said substrate (20) by total internal reflection; and at least one partially reflecting surface (22) located in said substrate (20).

Description

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Description " Light guide optical device "

FIELD OF THE INVENTION The present invention relates to substrate-guided optical devices, and in particular to devices including a plurality of reflection surfaces supported by a common light transmission substrate, also referred to as a light guide. The invention may advantageously be implemented in a large number of imaging applications, such as, for example, head-mount and head-up display ("head-up") display devices, cell phones, display devices compact, 3D display devices, compact beam expanders as well as non-imaging applications such as flat panel displays, compact illuminators, and scanners.

BACKGROUND OF THE INVENTION

One of the important applications of the compact optical elements is in head placement displays, wherein an optical module serves not only as an image lens but also as a combiner, in which a two-dimensional display device forms images for infinity and reflected to the eye of an observer. The display device may be obtained directly from a spatial light modulator (SLM), such as a cathode ray tube (CRT), a liquid crystal display (LCD) device, a cluster of organic light emitting diodes (OLED), or a scanning source and the like, or indirectly, by means of a correction lens or a bundle of optical fibers. The display device comprises a grouping of elements (pixels) that image to infinity by a collimation lens and are transmitted to the observer's eye by means of a reflection or partial reflection surface, which acts as a combiner for applications without combination of real and virtual (" non-see-through ") images and 2

ΕΡ 1 485 747 / EN combination of real and virtual (see-through) images, respectively. Typically, a conventional, free space optical module is used for these purposes. Unfortunately, as the desired field of view (FOV) of the system increases, such a conventional optical module becomes larger, heavier, bulky and therefore even for a moderate, impractical performance device. This is a major disadvantage for all types of display devices but especially for applications placed on the head, where the system must be as light and compact as possible. The search for increased compaction has led to several different complex optical solutions, for example, US 5,453,877 (Thomson-CSF) refers to an optical collimation system which is designed to be mounted on a helmet and allows overlapping information about the external landscape . The optical system comprises an optical device which is constructed of a transparent plate having two parallel faces and two parabolic mirrors at opposite ends. The collimated radiation strikes the first parabolic mirror through one of the parallel faces, is subsequently fully reflected by the first parabolic mirror, undergoes several full reflections on the parallel faces and is coupled outwardly through one of the parallel faces by means of the second parabolic mirror. The second parabolic mirror is partially transparent to permit the transmission of an external radiation by transparency.

Existing solutions on the one hand are not yet compact enough for most practical applications and on the other hand, suffer from major disadvantages in terms of manufacturing feasibility. Further, the mobility of the eye of the optical viewing angles resulting from these conceptions is usually very small, typically less than 8 mm. Therefore, the performance of the optical system is very sensitive even for small movements of the optical system relative to the eye of the observer and does not allow sufficient movement of the pupil to read text conveniently from such display devices. 3

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DISCLOSURE OF THE INVENTION The present invention facilitates the design and manufacture of very compact light-guiding optical elements (LOEs) for, among other applications, display devices for head placement. The invention enables relatively large FOV together with relatively large eye mobility box values. The resulting optical system offers a large, high-quality image that also entails large eye movements. The optical system offered by the present invention is particularly advantageous because it is substantially more compact than the prior art implementations and can still be incorporated immediately even in optical systems having specialized configurations. The invention also allows the construction of improved front view display (HUD) devices. Since the early days of such display devices for more than three decades, there has been significant progress in the field. In fact, HUDs have become popular and currently play an important role not only in modern combat aircraft but also in civil aircraft in which HUD systems have become a key component of low visibility landing operations. In addition, there have recently been numerous proposals and conceptions for HUD in applications for automobiles where potentially they can help the driver in the tasks of driving and navigation. However, prior art HUDs suffer from several significant disadvantages. All HUDs of the present designs require a display device source which must be spaced a significant distance from the combiner to ensure that the source illuminates the entire surface of the combiner. As a result, the HUD projector and combiner system is necessarily bulky and large and requires considerable installation space, which makes it inconvenient to install and sometimes unsafe to use. The large optical aperture of conventional HUDs also poses a considerable optical design challenge, causing HUDs to disengage from performance, or leading to high costs whenever high

ΕΡ 1 485 747 / PT. The high-quality holographic HUD scattering is of particular concern.

An important application of the present invention relates to its implementation in a compact HUD, which reduces the disadvantages mentioned above. In the HUD design of the present invention, the combiner is illuminated by a source of compact display device which can be attached to the substrate. Therefore, the complete system is very compact and can be installed immediately in a variety of configurations for a wide range of applications. In addition, the chromatic dispersion of the display device is negligible and as such may operate with large spectral sources, including a conventional white light source. In addition, the present invention expands the image so that the active area of the combiner may be much larger than the area that is actually illuminated by the light source.

Another important application of the present invention is to provide a large screen with a truly three-dimensional (3D) view. Progressive developments in information technology have led to an increased demand for 3D display devices. In fact, a wide range of 3D equipment is already on the market. However, the systems available require users to use special devices to separate the images that are intended for the left eye and the right eye. Such visual aid systems " were introduced with determination in many professional applications. However, expansion to other fields will require "free-view" systems " with improved visual comfort and greater adaptation to the mechanisms of binocular vision. State-of-the-art solutions to this problem suffer from several disadvantages and stand very close to familiar 2D display devices in terms of image quality and visual comfort. However, using the present invention it is possible to implement a true high quality 3D auto-stereoscopic display device which requires no visual aids and which can be manufactured immediately with standard optical manufacturing processes. 5

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A further application of the present invention is to provide a compact display device with a large FOV for handheld, mobile applications such as mobile phones. In the current market for wireless Internet access, sufficient bandwidth is available for full video streaming. The limiting factor remains the quality of the display device in the end-user device. Mobility requirements restrict the physical size of display devices and the result is a direct display device with poor image quality. The present invention allows a physically very compact display device with a very large virtual image. This is a key feature in mobile communications and especially for mobile internet access, solving one of the main limitations for its practical implementation.

By this means the present invention enables the digital content display of a full-featured Internet page within a small handheld device, such as a mobile phone.

Accordingly, the broad object of the present invention is to reduce the drawbacks of compact optical display devices of the prior art and to provide other systems and optical components that perform better according to specific requirements.

Accordingly the invention provides an optical device, comprising a light transmission substrate having at least two main surfaces and edges; optical means located on said substrate for coupling of light waves located in a given field of view on said substrate by total internal reflection and at least one partial reflection surface located on said substrate, said surface not being parallel to said main surfaces of the substrate. The partial reflection surface is an angularly selective flat reflection surface and is arranged so that the light waves located in said field of view reach both sides of said partial reflection surface. 6

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BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in connection with certain preferred embodiments, with reference to the following illustrative figures so that it can be better understood.

With specific reference to the figures in detail, it is pointed out that the particulars shown are by way of example only and for purposes of illustrative discussion of the preferred embodiments of the present invention and are presented in order to provide what is believed to be the most useful disclosure and which may be understood immediately from the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in greater detail than is necessary for a fundamental understanding of the invention. The description with the drawings serves as a guide for those of skill in the art as to how the various forms of the invention can be practically realized.

In the drawings: Fig. 1 is a side view of a generic form of the prior art folding optical device; Figure 2 is a side view of an exemplary light guide optical element according to the present invention; Figs. 3A and 3B illustrate the desired reflectance and transmittance characteristics of the selective reflection surfaces used in the present invention for two ranges of incidence angles; Fig. 4 shows the reflectance curves as a function of the wavelength for an exemplary dichroic coating; Fig. 5 shows a reflectance curve as a function of the angle of incidence for an exemplary dichroic coating; 7

Fig. 6 illustrates the reflectance curves as a function of the wavelength for another dichroic coating; Fig. Fig. 7 shows a reflectance curve as a function of the angle of incidence for another dichroic coating; Fig. 8 is a schematic sectional view of a reflective surface according to the present invention; Figs. 9A and 9B are diagrams illustrating detailed cross-sectional views of an exemplary array of selectively reflective surfaces; 10 is a diagram illustrating a detailed cross-sectional view of an exemplary array of selectively reflective surfaces wherein a thin transparent layer is cemented to the bottom of the light guide optical element; 11 illustrates detailed cross-sectional views of reflectance from an exemplary array of selectively reflective surfaces at three different viewing angles; Fig. 12 is a cross-sectional view of an exemplary device according to the present invention which utilizes a half wavelength plate to rotate the incoming light bias; Fig. 13 shows two graphs representing simulated calculations for brightness as a function of the FOV through the image of the projected display device and the external scene (viewed through); Fig. 14 is a diagram illustrating a light guide optical element (LOE) configuration, having a grouping of four partial reflection surfaces, in accordance with the present invention; FIG. 15 is a diagram illustrating a light guide optical element configuration having a grouping of four partial reflection surfaces, in accordance with another embodiment of the present invention; FIG. Fig. 16 is a diagram illustrating a method for expanding a beam along both axes using a dual LOE configuration; 17 is a side view of a device according to the present invention, which utilizes a liquid crystal display device (LCD) light source; 18 is a diagram illustrating an optical arrangement of an optical folding and collimation member in accordance with the present invention; Fig. 19 is a diagram illustrating the light projection region which is coupled to the substrate on the front surface of the collimation lens in accordance with the present invention; Fig. 20 is a diagram illustrating a diagram of an optical arrangement without bending, equivalent in accordance with the present invention; Fig. 21 is a diagram illustrating a diagram of an optical arrangement according to the present invention, which uses two pairs of parallel reflection mirrors to obtain a large field of view; Fig. 22A is a top view and 22B is a side view of an alternate configuration for expanding light according to the present invention; 23 illustrates an exemplary embodiment of the present invention embodied in a typical spectacle frame; 24 is a diagram illustrating an exemplary method for embodying an embodiment of the present invention within a mobile handheld device such as a mobile telephone; 9

Fig. 25 shows an exemplary HUD system according to the present invention; Fig. 26 shows an exemplary embodiment of the present invention wherein the light guide optical element is illuminated by a display device array; Figs. 27 to 29 are diagrams illustrating exemplary embodiments of an imaging system, which projects a three-dimensional image to the eyes of an observer, in accordance with the present invention; Fig. 30 illustrates one embodiment for conventional implementation of a stellar light amplifying device (SLA); Fig. 31 illustrates an exemplary embodiment for an improved implementation of the stellar light amplifier (SLA), which utilizes the devices according to the present invention; 32 is a side view of a device according to the present invention, which utilizes a display device for a reflective liquid crystal display (LCD) device with a conventional lighting device; 33 is a side view of a device according to the present invention, which utilizes a display device for a reflective liquid crystal display (LCD) device, in which a light guiding element is used to illuminate the source; Fig. 34 is a diagram illustrating a method of manufacturing a partial reflection surface assembly in accordance with the present invention; Fig. 35 is a diagram illustrating a metering arrangement that uses two prisms to measure the reflectance of a coated plate at two different angles and Fig.

36 is a diagram illustrating a metering system that uses two prisms to measure the reflectance of a coated plate at two different angles which further employs a folding prism to align the second output beam with the incoming input beam.

Fig. 1 illustrates a conventional folding optics arrangement, wherein the substrate 2 is illuminated by a source of display device 4. The display device is collimated by a collimation lens 6. The light of the display device source 4 is coupled to the substrate 2 by a first reflection surface 8 in such a way that the main radius 10 is parallel to the plane of the substrate. A second reflecting surface 12 engages light away from the substrate and into the eye of an observer 14. Although more compact of this configuration, it suffers from significant drawbacks; in particular, only a very limited FOV can be affected. As shown in Fig. 1, the maximum permissible angle relative to the axis within the substrate is:

arctang -l 2 /)

(D where T is the thickness of the substrate; double is the desired pupil exit diameter and 1 is the distance between reflection surfaces 8 and 12.

At angles greater than amax the rays are reflected from the substrate surface before they reach the reflection surface 12. Consequently, the reflection surface 12 will be illuminated in an unwanted direction and phantom images appear.

Therefore, the maximum FOV that is achieved with this configuration is: FOVmax ~ 2v. Oi max max (2) where V is the refractive index of the substrate. 11

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Typically the refractive index values are in the range of 1.5 to 1.6.

In a common way, the pupil diameter of the eye is 2 to 6 mm. To accommodate movement or misalignment of the display device, a large pupil outlet diameter is required. Considering the minimum desirable value of approximately 8 to 10 mm, the distance between the optical axis of the eye and the side of the head, 1, is typically between 40 and 80 mm. Consequently, even for a small FOV of 80, the desired substrate thickness would be of the order of 12 mm.

Methods have been proposed to overcome the above problem. These include the use of a magnifying telescope on the substrate and non-parallel coupling directions. However, even with these solutions and even if only one reflection surface is considered, the thickness of the system remains limited by a similar value. The FOV is limited by the diameter of the projection of the reflective surface 12 on the plane of the substrate. Mathematically, the maximum FOV that can be obtained due to this limitation is expressed as: FOVm

Ttmasur-dolho

R (3) eye in which asur is the angle between the reflective surface and the normal to the plane of the substrate and

Roiho is the distance between the eye of the observer and the substrate (typically about 30 to 40 mm).

Practically the tangasur can not be greater than 1; therefore, for the same parameters described above for a FOV of 8 °, here the thickness of the substrate required is in the order of 7 mm, which is an improvement over the previous limit. However, as the desired FOV is increased, the thickness of the substrate increases rapidly. For example, for desired FOVs of 15ø and 30ø the boundary thickness of the substrate is 18 mm or 25 mm, respectively.

To lessen the above limitations, the present invention utilizes a selective reflection surface array, 12

(1) and a light guide element (1). Fig. 2 shows a cross-sectional view of a LOE according to the present invention. The first reflection surface 16 is illuminated by a collimated display device 18 emanating from a light source (not shown) located behind the device. Reflection surface 16 reflects light incident from the source so that light is retained within a flat substrate 20 by total internal reflection. After various reflections from the surfaces of the substrate, the retained waves reach a cluster of selective reflection surfaces 22, which couple the light out of the substrate to the eye of an observer 24. Assuming that the center wave of the source is coupled outwardly of the substrate 20 in a direction normal to the substrate surface 26 and the angle of the wave coupled to the axis within the substrate 20 is ± n, so the angle asur2 between the reflection surfaces and normal to the plane of the substrate is:

(4)

As can be seen in Fig. 2, the retained rays reach the reflection surfaces from two distinct directions 28, 30. In this particular embodiment, the retained rays arrive at the reflection surface from one of these directions 28 following a an even number of reflections from the substrate surfaces 26, wherein the angle of incidence pref between the retained and normal radius of the reflection surface is:

The retained rays arrive at the reflection surface from the second direction 30 following an odd number of reflections from the substrate surfaces 26, where the angle with respect to the axis is a'in = 180 ° - ain and the angle of incidence between the retained ray and the normal ray reflection surface is: 90 ° + - (6) 2 β'rei = 90 ° (ain-asur2) = 90 ° (180 ° -in-asur2) 13

In order to prevent unwanted reflections and ghost images, it is important that the reflectance is negligible in one of these two directions. The desired discrimination between the two incidence directions can be obtained if one angle is significantly lower than the other. Two solutions to this requirement, both exploiting the reflection properties of the polarized light S were previously proposed, however, both solutions suffered from several disadvantages. The major drawback of the first solution is the relatively large number of reflection surfaces required to obtain an acceptable FOV. The main disadvantage of the second configuration is the unwanted reflectance of the radii having an internal angle of ain. An alternative solution is presently described which exploits the reflection properties of the polarized light P and in some cases also the polarized light S and which provides a smaller slope of the reflection surface so that fewer reflection surfaces are required for a given application.

The reflection characteristics as a function of the angle of incidence of the polarized light P and S are different.

Considering for example an air / crown glass interface; while both polarizations reflect 4% zero incidence, the Fresnel reflectance of the polarized light S incident on the boundary monotonously increases to reach 100% at the blending incidence, the Fresnel reflectance of the polarized light P first decreases to 0% in the Brewster angle and only then increases to 100% at the slope incidence. Accordingly, a high reflectance coating can be designed for polarized light S at an angle of oblique incidence and near-zero reflectance for a normal incidence. Furthermore, a coating for a P-polarized light with very low reflectance at high angles of incidence and a high reflectance at reduced angles of incidence could also be immediately conceived. This property can be exploited to prevent unwanted reflections and ghost images as described above by eliminating reflectance in one of the two directions. Choosing for example pref * 25 ° from Equations (5) and (6) can be calculated: P'ref = 105 °; ain = 130 °; ain 50Â °; (7) 14

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If a reflection surface is now determined for which β 'is not reflected but βθθ is, the desired condition is obtained. FIGS. 3A and 3B illustrate the desired reflectance behavior of the selective reflection surfaces. While the radius 32 (Fig. 3A) having an angle with reference to the axis of βΓθ * * ° is partially reflected and coupled out of the substrate 34, the radius 36 (Fig. 3B), which arrives at an angle with reference to the pivot axis ~ 75 ° with the reflection surface (which is equivalent to 3'ref '105 °), is transmitted through the reflection surface 34 without any noticeable reflection. 4 shows the reflectance curves of a dichroic coating designed to achieve the above reflectance characteristics at four different angles of incidence: 20 °, 25 °, 30 ° and 75 °, all for polarized light P. While reflectance of the high angle radius is negligible along the entire relevant spectrum, the radii at the angles with reference to the axis of 20 °, 25 ° and 30 ° obtain almost constant reflectance of 26%, 29% and 32% respectively, along the same spectrum. Evidently, the reflectance decreases with the obliquity of the incident rays. Fig. 5 shows the reflectance curves of the same dichroic coating as a function of the incident angle for polarized light P with the wavelength λ = 550 nm. Of course, there are two significant regions in this graph: between 50 ° and 80 ° where the reflectance is very low and between 15 ° and 40 ° where the reflectance monotonously increases with decreasing incidence angles. Therefore, since for a given FOV one can ensure that the entire angular spectrum of β ', where very low reflections are desired, will be located within the first region while the entire angular spectrum of β', where are required reflections, it will be located within the second region one can ensure the reflection of only one substrate mode for the eye of the observer and ensure an image without phantoms.

At this time, only polarized light P has been analyzed. This treatment is sufficient for a system that uses a source of polarized display device, such as a 15

(LCD) or to a system where output brightness is not critical and polarized light S can be filtered. However, for a non-polarized display device source, such as a CRT or an OLED and where the brightness is critical, the polarized light S can not be neglected and must be taken into account during the design procedure. Fortunately, although it is a greater challenge than polarized light P, it is also possible to design a coating having the same behavior for a polarized light S as discussed above. That is, a coating having a very low reflectance for an entire angular spectrum of β 'and higher predefined reflections for the respective angular spectrum of pref.

FIGS. 6 and 7 illustrate the reflectance curves of the same dichroic coating described above with reference to Figs. 4 and 5, but now for polarized light S. Apparently, there are some differences between the behavior of the two polarizations: the region of high angles where the reflectance is too low is narrower for the S polarization; it is much more difficult to obtain a constant reflectance at a given angle along the entire spectral bandwidth for the polarized light S than for the polarized light P; and finally, the monotonous behavior of the polarized light S in the angular spectrum of pref, where larger reflections are required, is opposite to that of the polarized light P, ie, the reflectance for the polarized light S increases with the obliquity of the incident rays. Apparently, this contradictory behavior of the two polarizations in the prefrontal spectrum could be used during the optical design of the system to obtain the desired reflectance of the total light according to the specific requirements of each system. It is clear that the reflectance of the first reflection surface 16 (Fig. 2) should be as high as possible so as to couple as lightly as possible from the display device source to the substrate. Assuming that the center wave of the source is normally incident on the substrate, i.e., at = 180 °, then the asurian angle between the first reflection surface and the normal to the plane of the substrate is:

ΕΡ 1 485 747 / PT Oísur 1 0 a 'sur 1 (8)

The solutions for asuri and a'SUri in the above example are 155 ° and 115 °, respectively. Fig. 8 shows a cross-sectional view of the reflective surface 16, which couples light 38 from a source of display device (not shown) and holds it inside the substrate 20 by total internal reflection. As shown here, the Si projection of the reflection surface on the substrate surface 40 is:

Si = T.tan (a) (9) where T is the thickness of the substrate. The α = αSuri solution is preferred, since the coupling area on the substrate surface for the above example is greater than 4.5 times that of the above solutions. A similar relationship improvement is maintained for other systems. Assuming that the coupled wave illuminates the entire surface of the reflection surface, after reflection from the surface 16, it illuminates an area of 2Si = 2Ttan (a) on the substrate surface. On the other hand, the projection of a reflection surface 22 on the plane of the substrate is S2 = Ttan (asur2). To prevent any overlapping or gaps between reflection surfaces, the projection of each surface is adjacent to its neighbor. Therefore, the number N of reflection surfaces 22 through which each coupled ray passes during a cycle (i.e., between two reflections from the same surface of the substrate) is:

N 25i S2 2r-tankaJ r.tan k ", :) (10)

In this example, where asur2 = 65 ° and asuri = 115 °, the solution is N = 2; that is, each radius passes through two different surfaces during a cycle. This is a conceptual change and a significant improvement over our previous descriptions, where each radius passes through six different surfaces during a cycle. The ability to reduce the number of reflection surfaces to a given FOV requirement refers to the projection of the reflection surface on the viewing plane - since the angles in the present description are larger, less reflection surfaces are required to transpose the image dimensions. Allowing fewer reflection surfaces simplifies LOE implementation and ensures significant cost savings in manufacturing. The embodiment described above with respect to Fig. 8 is an example of a method for coupling the input waves to the substrate. However, the input waves could also be coupled to the substrate by other optical means, including (but not limited to) folding prisms, optical fiber bundles, diffraction gratings and other solutions.

In addition, in the example shown in Fig. 2, the input waves and the image waves are located on the same side of the substrate. Other configurations are provided in which the image and input waves could be located on opposite sides of the substrate. It is also possible in certain applications to couple the incoming waves to the substrate through one of the peripheral sides of the substrate. Fig. 9A is a detailed cross-sectional view of a cluster of selectively reflective surfaces that engage light trapped inside the substrate and into the eye of an observer. As can be seen, in each cycle the coupled radius passes through the reflection surfaces 42 having a direction of ain = 130 °, whereby the angle between the radius and the normal to the reflection surfaces is * 75 ° and the reflections from these surfaces are negligible. In addition, the beam passes twice in each cycle through reflection surface 44 having a direction of ain = 50 °, where the angle of incidence is 25 ° and part of the radius energy is coupled out of the substrate. Assuming that a cluster of two selective reflection surfaces 22 is used for coupling light to the eye of an observer, the maximum FOV is: FOVm 2rtan «wl-d, eye

R (11) eye 18

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Therefore, for the same parameters of the above examples, the substrate boundary thickness for a FOV of 80 ° is of the order of 2.8 mm; for FOV of 15 ° and 30 °, the boundary thickness of the substrate is 3.7 mm and 5.6 mm, respectively. These are more favorable values than the threshold thickness of prior art solutions discussed above. In addition, more than two selective reflection surfaces may be used. For example, for three selective reflection surfaces 22, the substrate thickness for FOV of 15 ° and 30 ° is approximately 2.4 mm and 3.9 mm, respectively. Similarly, additional reflection surfaces can be introduced to, among other advantages, further reduce the optical thickness limit.

For configurations where a relatively small FOV is required, a single partial reflection surface may be sufficient. For example, for a system with the following parameters: R0iho = 25 mm; asur = 72 ° and T = 5 mm, a moderate FOV of 17 ° can be obtained even with a single reflection surface 22. Part of the rays will cross surface 22 several times before being coupled out in the desired direction. Since the minimum propagation angle within the substrate to obtain the total internal reflection condition for material BK7 or similar is α1η (ιηίη) = 42 °, the direction of propagation of the central angle of the FOV is ain (Cen) = 48 °. Consequently, the projected image is not normal to the surface but inclined 12 ° to the axis. However, for many applications this is acceptable.

As is shown in Fig. 9B, each selective reflection surface is illuminated by optical rays of different intensities. While the right surface 46 is illuminated by rays immediately after being reflected from the lower face 48 of the substrate 20, the left surface 50 is illuminated by rays which have already passed through the partial reflection surface 46 and are therefore of a lower intensity. In order to obtain uniform brightness images, compensation is required for the differences in intensities between the different portions of the image. In fact, the coating of the reflection surfaces with different coatings, whereby the surface reflectance 46 is 19

ΕΡ 1 485 747 / PT lower than the surface reflectance 50 compensates for uneven illumination.

Another potential non-uniformity may occur in the resulting image due to the different reflection sequences of different rays reaching each selective reflection surface: some rays arrive directly without a reflection from a selective reflection surface; other rays arrive after one or more such reflections. This effect is illustrated in Fig. 9A. A radius intersects the first selective reflection surface 22 at point 52. The angle of incidence of the radius is 25 ° and a portion of the energy of the radius is coupled out of the substrate. The radius then intersects the same selective reflection surface at point 42 at an angle of incidence of 75 ° without perceptible reflection and then intersects again at point 54 at an angle of incidence of 25 ° where another portion of the radius energy is coupled outwardly of the substrate. On the contrary, the radius, shown in Fig. 9B, experiences only a reflection from the same surface. We have noticed that more multiple reflections occur at smaller angles of incidence. Therefore, a method for compensating for the non-uniformity resulting from such multiple intersections is to design a coating where the reflectance monotonously increases with the decrease in the angle of incidence, as is shown in the reflectivity for the range 10 to 40 ° of Fig 5. It is difficult to fully compensate for such differences in the effects of multiple intersections. However, in practice, the human eye tolerates significant variations in luminosity that remain imperceptible. For display devices near the eye, the eye integrates all the light that emerges from a single viewing angle and focuses it on a point on the retina and since the response curve of the eye is logarithmic, small variations, if some of the brightness of the display device will not be noticeable. Therefore, even for moderate levels of uniformity of luminosity within the display device, a human eye experiences a high quality image. The required moderate uniformity can be obtained immediately with a LOE. 20

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However, for display devices located at a distance from the eye, such as front view display devices, non-uniformity due to the effects of multiple intersections can not be tolerated. For these cases, a more systematic method is needed to overcome non-uniformity. Fig. 10 illustrates a possible approach. A thin transparent layer 55 having a Tadd thickness is cemented to the bottom of the LOE. In this arrangement, the exemplary radius incident at 25 °, which according to Fig. 9A intersects the first selective reflection surface 22 at three points, intersects this surface only twice and is reflected only once: at point 52. Thus , the double reflection effect does not occur. The Tadd thickness can be calculated to minimize the double reflection effect for the entire FOV of the optical system. For example, for the optical system having the following parameters: FOV = 24 °; asur = 64 °; aln = 52 °; v = 1.51 and T = 4 mm, a layer having a thickness of Tadd = 2.1 mm should be added to completely eliminate the undesirable double-pass effect. Of course, the total thickness of the LOE is now 6.1 mm instead of 4 mm, but for HUD systems where the combiner is relatively large and a mechanical strength is required for the LOE, the greater thickness is not necessarily a disadvantage. It is possible to add the transparent layer to the top of the LOE or even on both sides of the substrate, where the exact configuration will be adjusted according to the specific requirements of the optical system. For the proposed configuration, no matter what the Tadd thickness, at least some of the radii intersect the same selective reflection surface twice. For example, in Fig. 10, the radius passes once through the first reflection surface 22 at point 52 having an angle of incidence of 25 ° where part of the energy of the radius is coupled out of the substrate and once at an angle of incidence of 75 ° without perceptible reflection. Of course, only the first intersection contributes to the image that is formed by the LOE.

FIG. 11 illustrates this effect: a cross-sectional view of a compact LOE display device system based on the proposed embodiment. FIG. 11 illustrates this effect: a cross-sectional view of a compact LOE display device system based on the proposed configuration. Here 21

A single plane wave 56 representing a particular viewing angle 58 illuminates only part of the total array of the partial reflection surfaces 22. Thus, for each point on the partial reflection surface, a nominal viewing angle and the reflectance is projected according to this angle. The design of the coatings of the various partially reflective surfaces of the LOE is performed as follows: for each particular angle, a ray is represented (taking into account the refraction due to Snell's law) from the center of the eye pupil considered 60 for surface of partial reflection. The calculated direction is defined as the nominal incident direction and the particular coating is designed according to that direction, also taking into account the prior reflectance related to this particular viewing angle. Therefore, for each viewing angle, the average reflectance from the relevant surfaces will be very close to the desired reflectance. In addition, if necessary, a layer of Tadd thickness will be added to the LOE.

A LOE with non-identical selective reflection surfaces has two consequences. In real and virtual (" see-through ") imaging systems, such as headlining display devices for pilots, where the observer should view the external scene through the LOE then reflectance reflectance should be relatively high. Since here the reflectance coefficient is not the same for all selective reflection surfaces, there is a danger of this also implying a non-uniform image of the external scene observed through the substrate. Fortunately, this non-uniformity is rather small and can be overlooked in many cases. In other situations, where such potential non-uniformity is crucial, a non-uniform complementary coating on the outer surface of the substrate could be added to compensate for non-uniformity of the substrate and obtain a uniform brightness view throughout the entire fove. 22

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In non-see-through (" non-see-through ") systems, such as virtual reality display devices, the substrate is opaque and system transmittance is unimportant. However, in such a case, the reflectance may be somewhat higher than previously and care must be taken to ensure that sufficient light passes through the first reflection surface in order to obtain uniform luminosity throughout the FOV . Another issue that must be taken into account is the polarization of light. As discussed above, polarized light P is preferred for coating the selective reflection surface. Fortunately, some of the compact display device sources (e.g., nematic liquid crystal display devices) are linearly polarized. This would also apply to situations where the display device source is oriented so that the incoming light is polarized S relative to the reflective surfaces. In such cases it is possible to design coatings for the polarized light S, or alternatively to rotate the polarization of the source with a half wave plate. As shown in Fig. 12, the light emerging from the display device source 4 is linearly polarized S. By using a half-wave plate 62, the bias is rotated such that the desired polarized light P is incident on the mating reflection surface 22.

To illustrate the expected performance of a typical real and virtual image combination system (" see-through "), a computer simulation was performed, which calculates the brightness not only of the projected display device but also of the external scene. The system has the following parameters: T = 4.3 mm; Tadd = 0; ain = 50 °; FOV = 24 °; R0ih0 = 25 mm; v = 1.51; the display device source is S-polarized, there are two selective reflection surfaces and the nominal reflectance is 22%. Fig. 13 shows the simulation results, normalized to the requested nominal values. There are some small fluctuations in both graphs but these changes would not be noticeable in applications near the eye.

So far, only the FOV has been discussed along the ξ axis. The FOV along the orthogonal axis η should also be considered. The FOV along the η axis is not dependent on the size or number of the selective reflection surfaces, but rather on the lateral dimension along the η axis of the coupled input waves in the substrate. The maximum FOV, which can be obtained along the axis η, is: FOVm D η ddho Ro, ko + l / (VÚnain) (12) where ϋη is the lateral dimension along the η axis of the coupled input waves in the substrate.

That is, if the desired FOV is 30 °, then using the same parameters described above, the lateral boundary dimension is 42 mm. It has been previously shown that the longitudinal dimension along the ξ axis of the coupled input waves in the substrate is provided by Si = Ttan (ain). A substrate thickness of T = 4 mm produces Si = 8.6 mm. Apparently, the lateral extent of the LOE is five times greater than the longitudinal dimension. Even for a 4: 3 picture aspect ratio (as with a common video display device) and the FOV on the η axis being 22 °, the required lateral dimension is approximately 34 mm, still four times larger than the dimension longitudinal. This asymmetry is problematic: - a collimating lens with a high numerical aperture, or a very large display device source is required. In any case, with such numerical dimension values, it is impossible to obtain the desired compact system.

An alternative method of solving this problem is shown in Fig. 14. Instead of using a pool of reflection surfaces 22 only along the axis ξ, another array of reflection surfaces 22a, 22b, 22c, 22d is positioned along of the η axis. These reflection surfaces are located normal to the plane of the substrate 20 along the bisector of the ξ and η axes. The reflectance of these surfaces is determined in order to obtain uniform output waves. For example, for four reflection surfaces, the reflectance of the surfaces should be 75%, 33%, 50% and 100% for the first surface 22a, the second surface 22b and the third surface 22c and the fourth surface 22d, 24E and 1 485 747 / PT respectively. This arrangement produces a sequence of wave fronts, each at 25% of the arrival intensity. Typically, such a reflection surface array can be readily designed for polarized light S. Fortunately, light that is polarized S compared to the partial reflection surfaces 22a to 22d will be polarized P as compared to the partial reflection surfaces 22 Therefore, if the vertical expansion of the image on the axis η is affected by polarized light S, there is no need for a half-wavelength plate to rotate the polarization of the light over the horizontal expands on the ξ axis. The arrangements shown in the die assemblies 22 and 22a to 22d are only examples. Further arrangements are possible to increase the lateral dimensions of the optical waves in both axes, according to the optical system and desired parameters, some of which are described below. Fig. 15 illustrates an alternative method for expanding the bundle along the η axis. In this configuration the reflectance of the surfaces 22a, 22b and 22c is 50% for polarized light S where 22d is a single 100% mirror. Although the lateral dimension of the vertical expansion for this solution is larger than in the previous configuration, it requires only a simple selective reflection coating and the overall configuration is easier to manufacture. In general, for each specific optical system the exact method for expanding the beam along the axis η can be chosen according to the particular requirements of the system.

Assuming a symmetrical collimation lens 6, the lateral dimension along the axis η after reflection from the reflective surfaces 22a to 22d, is provided by Ξη. = NTtan (ain), where N is the number of reflection surfaces. The maximum FOV that can be obtained along the η axis is now:

FOV n max

R η ^ iko iko iko iko iko Ro Ro Ro Ro Ro Ro iko +

Since the reflection array 22a to 22d can be located near the eye, the distance 1 between the reflection surfaces is expected to be smaller than in the previous examples. Assuming that 1 = 40 mm and choosing the 25 ΕΡ 1 485 747 / PT parameters: T = 4 mm; N = 4; ain = 65 °; R0iho = 25 mm and v = 1.5, the resulting FOV will be: FOvVx * 300 (14)

This is an improvement over previous values obtained above. Fig. 16 illustrates another method for expanding the beam along both axes using a double LOE configuration. The input wave is coupled into the first LOE 20a by the first reflection surface 16a and then propagates along the axis ξ. The partial reflection surfaces 22a couple the light out of 20a and then the light is coupled into the second LOE 20b by the reflection surface 16b. The light then propagates along the axis η and is then coupled outwardly by the selective reflection surfaces 22b. As shown, the original beam is expanded along both axes where the overall expansion is determined by the relationship between the lateral dimensions of the elements 16a and 22b respectively. The configuration provided in Fig. 16 is only one example of a dual LOE configuration. Other configurations are also possible where two or more LOEs are combined together to form complicated optical systems. For example, the three different substrates, each having been designed for one of three basic colors, can be combined to produce a three-color display device system. In this case, each substrate is transparent in relation to the other two colors. Such a system may be useful for applications in which a combination of three different monochrome display devices are required in order to create the final image. There are many other examples in which various substrates can be combined together to form a more complicated system.

Another issue to be addressed is the luminosity of the system. This issue is important for "see-through" virtual & image combination applications, where it is desired that the brightness of the display device is comparable to that of the external scene, to allow acceptable contrast ratio and convenient viewing through 26

ΕΡ 1 485 747 / PT. It can not be ensured that the insertion loss of most systems is small. For example, as described above for the four-surface combiner of Fig. 14, due to the required expansion of the beam along the η-axis, the optical wave brightness is reduced four times. In general for N reflection surfaces the brightness is reduced by a factor of N. In principle high light display devices can compensate for this difficulty, but this approach necessarily has a practical limitation. Not only are light source display devices very expensive, but they also have high power consumption with the associated very high electrical currents. Moreover, in most display devices there is an inherent limitation as to the maximum brightness that can be obtained. As an example, for LCD broadcasting, which are currently the most abundant source for small display devices, the power of backlight light is limited to prevent unwanted effects such as brightness that decreases the resolution and contrast ratio of the device display. Therefore, other approaches are needed to optimize the use of available light from the source.

One possible method for improving the brightness of the display device reaching the observer's eye is to control the reflectance of the reflection surfaces 22 of the LOE according to the observer's eye mobility (EMB) box. As is shown in Fig. 11, each reflection surface of the general array of selective reflection surfaces 22 is illuminated only by the general FOV. Therefore, the reflectance of each surface can be adjusted to optimize the brightness of the entire FOV. For example, the reflectance of the right surface 22a in Fig. 11 could be projected to have greater reflectance for the right portion of the FOV and the lowest possible reflectance for the left portion of the FOV, while the left surface 22b has higher reflectance for the left of FOV. A design method similar to a two-dimensional expansion system may be applied. Assuming that η is the vertical axis in Fig. 16, the reflectance of reflection surfaces 22a could be projected so that the lower surfaces are larger 27

Reflectance to the bottom of the FOV and the lowest possible reflectance to the top of the FOV, while the upper surfaces have higher reflectance to the top of the FOV. Accordingly, the factor that the brightness is reduced due to lateral expansion may be much smaller than R, where R is the ratio of the area of the input coupling surface 16a and the output coupling surfaces 22b.

Another method of improving overall system brightness is by controlling the brightness of the display device source without changing the input power. As shown in Fig. 11 above, a large portion of the energy coupled to the substrate 20 by the reflection mirror 16 is reflected into the pupil vicinity of the eye 60. However, in order to maximize the light that can be obtained, it is also desirable that the most of the light emerging from the display device source is coupled to the substrate. Fig. 17 shows an example of a substrate mode display device where the display device source is a transmitting LCD. The light emerges from the light source 64 and is collimated by a lens 66, illuminates an LCD 68. The image from the LCD is collimated and reflected by the optical components 70 onto the substrate 20. Fig. 18 illustrates an optical arrangement of the lens collimation / folding 70, while Fig. 19 illustrates the light projection region which is coupled to the substrate 20 on the front surface 72 of the lens 70. Typically, for most display device sources, there is a distribution Lambertian light, which emerges from the display device. That is, the energy is evenly distributed over the entire angular spectrum of 2n steradians. However, as can be seen in Figs. 18 and 19, only a small portion of the light emerging from the display device source is actually coupled to the substrate 20. From each point source on the surface of the display device, only a small cone of light from * 20 to 30 Actually illuminates the projection zone on the front surface 72 and engages the substrate 20. Consequently, a significant increase in brightness can be obtained if the light emerging from the display device is concentrated within this cone. 28

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One method of achieving such directionality in source illumination is to use a special selective diffuser for the LCD. Normally, a conventional diffuser spreads light evenly in all directions. Alternatively, a selective diffuser can spread the light in such a way that light from each point source diverges in a desired angular cone. In this case the energy that the LCD surface illuminates remains the same. For a cone of 20 to 30 °, the angle of light divergence for each point source is reduced by a factor of more than 50 when compared to the steradian π of the Lambertian source, the light brightness increases the same factor. Therefore, a significant improvement in the brightness of the system can be achieved with minimal design and manufacturing effort and without increasing the system's power consumption.

One workaround, which is appropriate not only for LCD but also for other display device sources, is to use a microlens array that is aligned with the pixels of the display device source. For each pixel a microlens narrows the divergent beam that emerges from that pixel at the desired angular cone. In fact, this solution is effective only if the pixel form factor is a small number. An improved version of this solution is to design the pixel emission distribution function in the pixel grouping to make each pixel diverge with the desired angle. For example, in OLED display devices, efforts are usually made to increase the angle of divergence of single LEDs to allow viewing from a large angle. However, for our specific application of LOE display device, it is advantageous to keep this angle of divergence small, in the range of 20 to 30ø, to optimize the brightness of the system.

As described above, with reference to Figs. 14 and 15, it is possible to obtain a larger FOV also along the vertical direction η without increasing the system volume significantly. However, there are situations where this solution is not enough. This is especially true for systems with a very large FOV and a constraint over the distance 1 between the input coupling reflective surface 16 and the selective reflection surfaces of 29

Fig. 20 illustrates an unopened optical system with the following parameters: 1 = 70 mm; T = 4 mm; aln = 65 °; R0iho = 24 mm; v = 1.51, the eye mobility box (EMB) is 10 mm and the intended vertical FOV is 42 °. If we follow the rays from the EMB 74, we will find that the light passes through the EMB projection onto the output coupling optic 22, where 76, 78 and 80 are the projections of the upper, central and lower angles respectively of the FOV . This means that to obtain the desired FOV the required input coupling aperture 82 is 65 mm; this is a very large aperture that necessarily increases the size of the entire system, even if the substrate remains a thin plate. Alternatively, if only a smaller aperture 84 of 40 mm is allowed, the vertical FOV obtainable 86 drops to 23 ° which is almost half of the desired FOV. Fig. 21 illustrates a possible solution to this problem. Instead of using a simple rectangular plate 20, the two horizontal edges of the plates are replaced by two pairs of parallel reflection surfaces, 88a, 88b and 90a, 90b respectively. While the central portion of the FOV projects directly through the aperture 84 as above, the lower FOV rays are reflected from the surfaces 88a and 88b, while the upper FOV radii are reflected from the surfaces 90a and 90b . Typically, the angles between the rays retained within the substrate and the reflection surfaces 88 and 90 are large enough to affect the total internal reflections, thus no special reflection coating is required for these surfaces. Since all of the radii move directly from the entry aperture or are reflected twice from a pair of parallel surfaces, the original direction of each radius is maintained and the original image is not affected.

In fact, it is important to ensure that each radius that is reflected by the surface 88a is also reflected by the surface 88b before engaging the aperture 84. To confirm this, it is sufficient to check two radii paths: - the marginal radius of the incident incident end angle 92 on the surface 88a at point 94, has to strike the surface 88b to the right of its intersection with 30

Surface 90a; in addition, the marginal radius 96 incident on the surface 88a following its intersection 98 with the surface 90b must be incident on the surface 88b before crossing the aperture 84. Since both marginal radii meet the requirement, the rays from the FOV that are incident on the surface 88a will also be incident on the surface 88b. The present example provides a 42 ° FOV with a significantly reduced inlet aperture of 84:40 mm. Of course, in cases where 1 is extremely large, a cascade of two or more pairs of reflection surfaces may be used to obtain the desired FOV while maintaining an acceptable inlet aperture. The embodiment of Fig. 21 is only an example illustrating a simple implementation of this method. The use of pairs of parallel reflection surfaces in order to decrease the aperture of the system to a given FOV, or alternatively to increase the FOV that may be used for a given aperture, is not limited to the substrate mode optics and may be used in other optical systems including, but not limited to, free space systems such as front view display devices, episcopes or periscopes.

Apparently, as described above with reference to Fig. 21, the side dimension of the substrate inlet aperture is 40 mm along the η axis and 8.5 mm along the ξ axis. FIGS. 22A and 22B illustrate an alternative embodiment to that described above with reference to Figs. 14 to 15. This approach involves an adjustment between a symmetrical collimating lens 6 and an asymmetric inlet aperture. The lateral dimensions of the inlet opening are assumed to be D and 4D along the two axes respectively. A lens 6 having a 2D aperture will collimate the image on the substrate. The front half of the collimated light is coupled to the substrate by the mirror 16a. Two pairs of parallel reflection surfaces, 22a; 22b and 22c; 22d divide the coupled light outwardly and then reflect it back to its original direction. The back side of the collimated light passes through the substrate 20 and then the prism 99 is folded back into the substrate. A second mirror 16b engages the folding light 31

In the substrate 20. Of course, the side dimensions of the inlet aperture are D and 4D along the two axes respectively, as desired.

There are some advantages to the approach described above with reference to Fig. 22. The system is symmetrical about the axis η and more importantly, there is no loss of light intensity. This approach is only an example and other similar methods are possible for converting the symmetrical input beam into an asymmetric coupled light beam. A suitable configuration for expanding the image along the η axis requires careful analysis of the system specifications.

In general, all of the different configurations of the light guide optical elements considered above offer several important advantages over alternative compact optics for display device applications, which include: 1) The input display source device can be located very close to the substrate, so that the overall optical system is very compact and lightweight, offering an unmatched form factor. 2) In contrast to other compact display device configurations, the present invention provides flexibility in locating the source of input display device relative to the eyepiece. This flexibility, combined with the ability to locate the source near the expansion substrate, lessens the need to utilize an off-axis optical array that is common to other display device systems. In addition, since the inlet aperture of the LOE is much less than the active area of the aperture aperture, the numerical aperture of the collimation lens 6 is much less than that required for a comparable conventional imaging system. Accordingly, a significantly more convenient optical system and the many difficulties associated with off-axis optics and high numerical aperture lenses can be implemented, such as aberrations 32

And field conditions can be compensated relatively easily and efficiently. 3) The reflectance coefficients of the selectively reflective surfaces in the present invention are essentially identical over the entire relevant spectrum. Accordingly, light sources, not only monochromatic but also polychromatic, may be used as display device sources. The LOE has a negligible wavelength dependency that ensures high-quality color display devices with high resolutions. 4) Since each point of the input display device is transformed into a flat wave that is reflected to the observer's eye from a large part of the reflection array, tolerances for the exact location of the eye can be significantly enlarged. As such, the viewer can see the entire field of view and the eye mobility box can be significantly larger than in other compact display device configurations. 5) Since a large part of the intensity of the display device source is coupled to the substrate and since a large portion of this coupled energy is " recycled " and coupled outwardly to the eye of the observer, a comparatively high brightness display device can be obtained even with low power consumption display sources. 23 illustrates one embodiment of the present invention in which the LOE 20 is incorporated into a spectacle frame 100. The display device source 4, the collimation lens 6 and the folding lens 70 are mounted within the stem portions 102 of the spectacle frame, even after the edge of the LOE 20. For a case in which the display device source is an electronic element such as a small CRT, LCD, or OLED, the drive electronics 104 for the source The display device may be mounted within the rear portion of the rod 102. A power supply 33

The data interface 106 may be connected to the stem 102 by a lead wire 108 or other communication means including radio or optical transmission. Alternatively, a battery and miniature data link electronics may be integrated into the spectacle frame. The embodiment described above can serve not only for real and virtual image combination systems (" see-through ") but also for non-see-through " virtual image combining. In the latter case, opaque layers are located in front of the LOE. It is not necessary to occlude the entire LOE, typically only the active area where the display device is visible needs to be locked. As such, the device can ensure that the peripheral vision of the user is maintained by copying the visual experience of a computer or television screen in which such peripheral vision plays an important cognitive function. Alternatively, a variable filter may be placed in front of the system in such a way that the observer can control the level of lightness of the light emerging from the outer scene. This variable filter could be a mechanically controlled device such as a folding filter, or two rotating polarizers, an electronically controlled device, or even an automatic device, whereby the transmittance of the filter is determined by the brightness of the outer bottom.

There are some alternatives as to the precise way that a LOE can be used in this embodiment. The simplest option is to use a single element for an eye. Another option is to use one element and one display device source for each eye, but with the same image: Alternatively it is possible to project two different parts of the same image, with some overlap between the two eyes, allowing a larger FOV. Still another possibility is to project two different scenes, one for each eye, in order to create a stereoscopic image. With this alternative, attractive implementations are possible, including three-dimensional movies, advanced virtual reality, training systems and others. The embodiment of Fig. 23 is only one example illustrating the simple implementation of the present invention. Since the 34

The substrate-guided optical element, which is the core of the system, is very compact and lightweight, could be installed in a wide variety of arrangements. Accordingly, many other embodiments are also possible including a display device, a folding display device, a monocle and many more. This embodiment is designed for applications where the display device should be close to the eye; placed on the head, used on the head or carried by the head. However, there are applications where the display device is located differently. An example of such an application is a handheld device for mobile application, such as for example a mobile phone. These devices are expected to undertake new operations in the near future, requiring the resolution of a large screen, including video phone, Internet connection, e-mail access and even high-quality satellite TV transmission. With existing technologies, a small display device could be incorporated into the interior of the telephone, however, such a display device can only project poor video data, or a few Internet or e-mail data lines directly into the eye . 24 shows an alternative method, based on the present invention, which eliminates the present compromise between the small size of the mobile devices and the desire to view digital content in a full format display device by projecting high quality images directly into the user's eye. An optical module including the display device source 6, the collimation and folding optics 70 and the substrate 20 is integrated into the body of a mobile phone 110, where the substrate 20 replaces the protective cover window of the telephone. Specifically, the volume of carrier components including source 6 and optics 70 is sufficiently small to mount within an acceptable volume for modern mobile telephone devices. To observe the entire screen transmitted by the device the user positions the window in front of his eye 24, to conveniently observe the image with high FOV, a large eye mobility box and a comfortable pupil spacing. It is also possible to observe the entire FOV at a distance of 35

The pupil larger when tilting the device to display different portions of the image. In addition, since the optical module can operate in both real and virtual image combination configuration (" see-through "), dual device operation is possible; namely it is optionally possible to maintain intact the conventional mobile phone display device 112. In this way the common low-resolution display device can be observed through the LOE when the display device source 6 is switched off. In a second mode, designed to read e-mail, internet search, or video operation, the conventional display device 112 is turned off while the display device source 6 projects the desired large FOV image into the observer's eye through the LOE. The embodiment described in Fig. 24 is only one example, which illustrates that other applications than the display devices for head placement may be embodied. Other possible portable provisions include pocket computers, small display devices embedded in wristwatches, a display device that can be carried in a pocket that has the size and weight remaining of a credit card and many more.

The embodiments described above are monocular optical systems, i.e., the image is projected into a single eye. However, there are applications, such as front-view display devices (HUDs), where you want to project an image in both eyes. Until recently, HUD systems were mainly used in advanced civilian and combat aircraft. There have been numerous proposals and conceptions of the latter to install a HUD in front of a car driver to assist in navigation while driving or to project a thermal image in your eyes during low visibility conditions. Current HUD aerospace systems are very costly, the price of a single unit being in the hundreds of thousands of dollars. In addition, the existing systems are very large, heavy and bulky and are also complicated to install on a smaller aircraft in a car. LOUD-based HUDs potentially provide the possibilities for an autonomous, very compact HUD that can be installed immediately in confined spaces. It also simplifies the construction and 36

And is therefore potentially suitable not only to improve aerospace HUDs, but also to introduce an inexpensive, compact, consumer version for the automotive industry. 25 shows a method of materializing a HUD system based on the present invention. The light from a display device source 4 is collimated by a lens 6 to infinity and coupled through the first reflection surface 16 on the substrate 20. Following the reflection, in a second reflection array (not shown), the optical waves engage a third reflecting surface 22, which engages the light outwardly into the observer's eyes 24. The overall system can be very compact and lightweight, the size of a large postcard that has a thickness of a few millimeters. The display device source, which has a volume of a few cubic centimeters, can be attached to one of the corners of the substrate, where an electric wire can transmit power and data to the system. It is expected that the installation of the HUD system presented will not be more complicated than the installation of a simple commercial audio system. Further, since there is no need for an external display device source for image projection, the need to install components in unsafe locations is avoided.

Since the pupil output of a typical HUD system is much larger than that of a system placed on the head, it is expected to require a three die configuration as described above with reference to Figs. 14 to 16, to obtain the desired FOV. However, there may be some special cases, which include systems with small vertical FOVs, or with a vertical LED array as a display device source, or by scanning pairs of parallel reflection mirrors (as described above with reference to Fig. ), in which a configuration of two matrices would suffice.

The embodiments shown in Fig. 25 may be implemented for other applications in addition to HUD vehicle systems. One possible use of these embodiments is a flat display device for a 37

ΕΡ 1 485 747 / EN computer or television. The only main feature of such a display device is that the image is not located in the plane of the screen but is focused to infinity or to an equally convenient distance. One of the major disadvantages of existing computer display devices is that the user has to focus their eyes at a very short distance between 40 and 60 cm while the natural focus of a healthy eye is towards infinity. Many people suffer from headaches after working for a long period of time on a computer. Many others who often work with computers tend to develop myopia. In addition, some people, who suffer not only from myopia but also farsightedness, need special glasses to work with a computer. A flat display device based on the present invention could be a suitable solution for people suffering from the problems described above and do not wish to work with a display device placed on the head. Further, the present invention allows for a significant reduction in the physical size of the screen. Since the image formed by the LOE is larger than the device, it would be possible to implement large screens in smaller frames. This is particularly important for mobile applications such as pocket computers and laptops.

A potential problem that can arise with a large display device LOE refers to its brightness. Ideally, for increased compactness it is advantageous to use a source of miniature display device, but this necessarily reduces the brightness of the display device due to the large increase in the actively illuminated area of the LOE when compared to the actively illuminated area of the source. Therefore, even after the special measures described above are available, a reduction in brightness is expected, even for non-see-through ('non-see-through') applications. This reduction in brightness can be negated by increasing the brightness of the source, or having more than one source available. That is, LOE can be illuminated with a grouping of display device fonts and their associated collimation lenses. 26 shows an example of this method. The same image is generated from a grouping of 4 sources 38

4a to 4d, each collimated by a grouping of lenses 6a to 6d related to form a single collimated image, which is coupled to the LOE 20 by reflection surface 16. At first sight it appears that this solution can be very costly. Here any increase in the cost of the system by increasing its components and the need to coordinate the images of the sources with special electronics is negated by the inherently low cost of the display microdisposers themselves and the ability to reduce the numerical aperture of the collimation lenses. There is also no need for any side expander in this arrangement; it is quite feasible to include only one LOE image expander of one dimension and to increase the brightness accordingly. It is important to note that the display device fonts do not necessarily have to be identical to each other and a more complicated system with different display device fonts may be used as explained below.

Another advantage of the LOE display device of the present invention is its very flat shape, even compared to the existing flat panel display devices. Another difference is a significantly more directional viewing angle: the LOE display device can be observed from a significantly limited angular range when compared to the common flat panel display device. Such a limited head mobility box is sufficient for convenient operation by a single user and offers the additional privacy advantages in many situations.

In addition, the LOE-based screen image is located in a plane far behind the surface of the display device and not on its physical surface. The feel of the image is similar to watching it through a window. This configuration is particularly suitable for implementing three-dimensional display devices.

Progressive developments in information technology have led to an increased demand for 3D display devices. In fact, a wide range of 3D equipment is already on the market. However, the systems available

ΕΡ 1 485 747 / EN the use of special devices to separate the images intended for the left eye and the right eye. Such visual aid systems " were implemented with determination in many professional applications. However, expansion to other fields will require "free-view" systems " with improved visual comfort and greater adaptation to the mechanisms of binocular vision. The current solutions to this problem suffer from several disadvantages and stand behind the familiar 2D display devices in terms of image quality and viewing comfort.

FIGS. 27A and 27B show a front view and a top view, respectively, of a possible configuration, based on the present invention to realize a truly 3D display device. Instead of a single display device source, a pool 114 of n different display device sources 114i 114n is located in the lower portion of the substrate 20, where each display device source projects images obtained in different perspectives of the same scene . The image from each display device source is coupled to the substrate in the same manner as described above with reference to Fig. 26. When the observer is observing the display device, his right eye 24a and left 24b see the images projected from the display device sources 114i and 114j, respectively. Consequently the observer sees with each eye the same scene from a different perspective. The experience almost resembles the visual experience when viewing a really 3D object through a window. As is shown in Figs. 28a to 28b, when the viewer moves his gaze horizontally his eyes come from images that are projected from different sources of display device 114k and 114i; the effect is similar to moving your head through a window while looking at an external scene. When the observer moves his gaze vertically, as is shown in Figs. 29A to 29B, the eyes see spots on the screen that are located lower than before. Since these points are located closer to the display device sources 114, the observer sees images that emerge from different display device sources 114g and 114h, which are located at 40

1 485 747 / PT closer to the center of the assembly 114 than before. As a result, the viewer's sensation is similar to seeing a scene, which is closer to the window. That is, the scene through the substrate is seen as a three-dimensional panorama where the bottom of the scene is closer to the observer. The embodiment described above with respect to Figs. 27 to 29 is just one example. Further arrangements are also possible to realize a truly 3D display device with different apertures, number of aspect points and more in using the present invention.

Another possible embodiment of the invention is its implementation as a telepoint, such as that used to project text to a speaker or TV presenter; as the telepile is transparent, the audience thinks the speaker is having eye contact with it while he is actually reading the text. Using a LOE, the telepoint can be implemented with a small source, fixed to the optical assembly, avoiding the need to locate a large screen in the neighborhood of the device.

Yet another possible implementation of this embodiment is as a screen for a personal digital assistant (PDA). The size of the existing conventional screens, which are currently used, is less than 10 cm. Since the minimum distance to which these display devices can be read is on the order of 40 cm, the FOV obtained is less than 15 °; therefore, the content of information, especially with respect to text, in these display devices is limited. A significant improvement in the projected FOV can be realized with the embodiment shown in Fig. 24. The image is focused to infinity and the screen may be located closer to the observer's eyes. In addition, since each eye sees a different part of the total field of view (TFOV) with an overlap in its center, another increase in TFOV can be obtained. Therefore, a display device with a FOV of 40 ° or higher is feasible.

In all of the embodiments of the invention described above, the image which was transmitted by the substrate 20, was generated at 41

From an electronic display device source such as a CRT or LCD. However, there are applications where the transmitted image may be a part of a live scene, for example, how much is required to couple a live scene in an optical system. 30 shows an application of a stellar light amplifier (SLA) 116 where this implementation is desired. The image from the outer scene is focused by the collimator 118 in the SLA where the electronic image signal is amplified to create a synthetic image which is projected through an eyepiece 120 into the eye of the observer. The illustrated configuration is fairly popular for military, paramilitary and civilian applications. This normally used configuration necessarily protrudes forwardly in front of the user and makes it inconvenient for prolonged use in a configuration placed on the head. The device is relatively heavy and in addition to its physical interference with objects in the vicinity of the user and exerts a forceful moment on the head and neck of the wearer.

A more convenient configuration is illustrated in Fig. 31. Here the device is not located in front of the user but at the side of the head where the center of gravity of the SLA is aligned along the main axis of the head. The direction of the device is reversed, i.e. the collimator 118 is located at the rear and the eyepiece 120 is located at the front. The image from the front outer scene is now coupled into the collimator 118 by using a LOE 20a, where the image from the eyepiece 120 is coupled into the eye of the observer when another LOE 20b is used. Although two additional optical elements 20a and 20b are added to the original device, the weight of these elements is negligible compared to the weight of the SLA and the overall configuration is much more convenient than before. Furthermore, since the mounting tolerance of these devices is far more demanding, it is feasible for these two elements to be configured as a module so that they can be changed from their position or even removed by the user. In this way the SLA observer can be reconfigured for convenient location for operation placed on the head with LOE 42

ΕΡ 1 485 747 / EN, or to mount on standard weapon sites or other sight devices to be used without the LOE module. It is also possible to change the LOE to accommodate the use of the device with any eye.

In all of the above embodiments, the LOE is used to transmit light waves for imaging purposes. However, the present invention can be applied not only for imaging, but also for non-imaging applications, especially lighting systems, in which the optical quality of the output wave is not crucial and the important parameters are uniform intensity and luminosity. The invention may be applied, for example, in backlighting of flat panel display devices, most of which are LCD systems, in which, in order to construct an image, it is necessary to illuminate the board with a brighter and uniform light possible. Other such possible applications include, but are not limited to, flat and inexpensive substitutes for spotlighting or floodlighting, fingerprint digitizing illuminators, and wave readers for three dimensional display holograms.

One of the uses of lighting that can be considerably improved when using a LOE device is for a reflective LCD. 32 shows an example of a substrate mode display device where the display device source is a reflection LCD. The light generated by an illuminator 122 passes through a polarizer 124, collimated by a lens 126, reflected by a polarization beam separator 128 and illuminates a LCD 130. The polarization of the light that is reflected from the LCD is rotated through 90 ° by a 1/4 wavelength plate, or alternatively by the LCD material itself. The image from the LCD passes through the beam separator to be collimated and reflected by the lens 132 onto the substrate 20. As a result of the beam separator configuration, the entire lighting system is large and cumbersome, and certainly not compact enough for head placement systems. Further, due to the beam separator 128 the collimation lens 132 is located further away from the display device source, while to minimize aberrations 43

ΕΡ 1 485 747 / EN that the field lenses are located as close as possible to the surface of the display device.

An improved version of the illumination configuration is illustrated in Fig. 33. The light from the light source 122 is coupled into another LOE 134, which illuminates the surface of the LCD 130, where the partially reflective surfaces are polarization sensitive . Apparently, the entire system here is much more compact than that shown in Fig. 32 and the lens 132 is located much closer to the surface of the LCD. In addition, since the inlet aperture of the LOE 134 is much smaller than that of the beam separator 128, the collimation lens 126 may now be much smaller than before and hence have a larger f-number. The illumination arrangement shown in Fig. 32 is only an example. Other provisions are also permitted for the illumination of a reflective or transmission LCD, or for use in any other lighting purpose according to the optical system and desired parameters.

An important issue which should be referred to is the manufacturing process of the LOE, where the crucial component is the grouping of selective reflection surfaces 22. Fig. 34 illustrates a possible method of manufacturing a grouping of partial reflection surfaces. The surfaces of a plurality of transparent flat plates 138 are coated with the necessary coatings 140 and then the plates are cemented together so as to create a stacked shape 142. A segment 144 is then cut into slice from the cut stacked form, grinding, and polishing to create the desired pool of reflection surfaces 146, which can be assembled with other elements to materialize the entire LOE. More than one array 146 may be fabricated from each segment 144, according to the actual size of the coated plates 138 and the desired size of the LOE. As was described in Figs. 4 to 7, the desired coatings of the selective reflection surfaces must have a specific spectral and angular response in order to ensure proper operation of the LOE. Therefore, it is essential to accurately measure the actual performance of the coatings prior to the final fabrication of the LOE. As explained above, there are two angular regions that should be measured - the 44

(Usually between 60 ° and 85 °) where the reflectance is very low and the angles of incidence reduced (usually between 15 ° and 40 °), where surface reflectance is used for coupling of part of the waves retained outside the LOE. Naturally, the coating should be measured in these two regions. The main problem with the test procedure is that it is very difficult to measure with the existing test equipment the reflectance (or alternatively the transmission) at very high angles of incidence, usually above 60 °, for coatings that are located, as in our case , between two transparent plates. Fig. 35 illustrates a proposed method for measuring reflection of a coated surface 150 at very high incidence angles. Initially two prisms 152 with an angle α are fixed to the coated plate. The arrival beam 154 strikes the coated plate at an angle of incidence a. Part of the bundle 156 continues in the original direction and its intensity Ta can be measured. Therefore, given the Fresnel reflections from the outer surface, the reflectance of the coating measured at an angle α can be calculated as Ra = 1-Ta. In addition, the other part of the beam is reflected from the coated surface, again reflected by total internal reflection from the outer surface of the lower prism, striking the coated surface again at an angle 3a, reflected again from the outer surface of the upper prism by total internal reflection and then reflected by the coated surface at an angle α and coupled out of the prism. Here, the output beam intensity 158 can be measured. Considering Fresnel's reflections, the intensity of the output beam is (Κα) 2 * Τ3θί. Therefore, since the reflectance Ra is known from the previous step, the reflectance at an angle 3a can consequently be calculated. There are test equipment where the output beam must be located on the same axis as the arrival beam. 36 shows a folding prism 160 used for translation movement of the beam in the original beam. The residue of the original ray 154 may be blocked using a suitable locking layer or mask 162. 45

ΕΡ 1 485 747 / EN

Of course, each pair of prisms can measure the reflectance at two angles -a and 3a. For example, if the main angle is 25 ° then the reflectance at 25 ° and 75 ° can be measured simultaneously. Therefore, a small number of pairs of prisms (2 or 3) are normally required for proper measurement of the coated plates. Of course, the configuration shown here can be used to measure the reflectance of these two angles at different wavelengths as well as for the two polarizations, if necessary.

It will be apparent to those skilled in the art that the invention is not limited to the details of the embodiments illustrated above and that the present invention may be embodied in other specific forms. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims instead of the foregoing description and all such changes which may be within the meaning and extent of equivalence of the claims are therefore intended to be covered by them.

Lisbon

Claims (43)

An optical device, comprising: a light transmission substrate (20) having at least two main surfaces (26), parallel to each other, and edges; means (16) located on said substrate (20) for coupling light waves, located in a given field of view on said substrate (20) by total internal reflection, and at least one partial reflection surface (22), located on the substrate (20), said surface (22) not being parallel to said major surfaces (26) of the substrate (20), characterized in that said partial reflection surface (22) is an angularly selective and flat reflection surface, and in that said partial reflection surface (22) is arranged such that light waves located in said field of view arrive on both sides (42, 44) of said partial reflection surface (22). An optical device according to claim 1, wherein said optical means (16) for light coupling on said substrate (20) are arranged at an angle to said main surfaces (26) to cause at least one , part of the light rays of said coupled light intersect said partial reflection surface (22) at least two times at two different angles of incidence, before being coupled off said substrate (20). An optical device according to claim 1 or 2, wherein said reflection surface (22) is disposed within said substrate (20) at an angle greater than the angle to the axis of the coupled light waves in the substrate 20, whereby the radii of said coupled light waves incident on a side 42 of the surface 22 with a first angle of incidence and rays of said coupled light waves engage a second side (44) of said surface (22) at a second minor angle of incidence. An optical device according to one of claims 1 to 3, in which said partial and angularly selective reflection surface (22) causes a small reflection for one part of the angular spectrum and a large reflection for the other parts of the angular spectrum. An optical device according to claim 4, wherein said partially angularly selective reflection surface (22) causes a low reflectance with high incidence angles and a high reflectance at reduced angles of incidence. An optical device according to claim 3, wherein said partially angularly selective reflection surface (22) causes a small reflection at one of said angles of incidence and a significantly greater reflection for the second of said angles of incidence. An optical device according to claim 3, wherein said first angle of incidence, which has a small reflectance, is greater than said second angle of incidence. Optical device according to one of Claims 1 to 7, in which a grouping of two or more partial reflection surfaces (22) is provided, characterized in that said partial reflection surfaces (22) are parallel to each other and are not parallel to any one of the edges of said main surfaces (26) of the substrate (20). An optical device according to one of claims 1 to 8, wherein said optical means (16) comprises a wave reflection surface, located on said substrate (20). An optical device according to any one of claims 1 to 9, wherein said at least one partial reflection surface (22) engages the light retained by total internal reflection outside the said substrate (20). An optical device according to one of claims 1 to 10, further comprising means for producing output light waves from incoming light waves, wherein said incoming light waves and the light waves of are located on the same side of said substrate (20). An optical device according to one of claims 1 to 10, further comprising means for producing output light waves from incoming light waves, wherein said incoming light waves are located on one side of said light source (20) and said output light waves are located on the other side of said substrate (20) The optical device of one of claims 1 to 10, further comprising means for producing output light waves from incoming light waves, wherein said incoming light waves are coupled on said substrate ( 20) through one of its edges. An optical device according to claim 8, wherein the reflectance of each of said partial reflection surfaces (22) is not identical across the reflection surfaces (22). An optical device according to one of claims 1 to 14, wherein said partial reflection surface (22) has a polarized light jacket P. An optical device according to one of claims 1 to 14, wherein said partial reflection surface (22) has a coating for a polarized light S. An optical device according to one of claims 1 to 14, wherein said partial reflection surface (22) has a coating for a non-polarized light. ΕΡ 1 485 747 / ΡΤ 4/7 An optical device according to one of claims 1 to 17, further comprising a second set of one or more reflection or partial reflection surfaces, located on said substrate (20), said partial reflection surfaces of the second set parallel to each other and not at least parallel to said at least one partial reflection surface (22). An optical device according to claim 18, wherein said second set of reflection or partial reflection surfaces alters the direction of light propagation coupled in said substrate (20) by total internal reflection. An optical device according to claim 18 or 19, wherein the reflectance of said second plurality of partial reflection surfaces produces a field of view having a uniform brightness profile. Optical device according to one of Claims 1 to 20, further comprising at least one pair of reflection surfaces supported by said substrate (20), said reflection surfaces of the pair being parallel to each other and being part of the edges of said substrate (20). The optical device of claim 21, wherein said at least one pair of reflection surfaces alters the direction of propagation of light, coupled on said substrate (20) by total internal reflection and then reflects the same again for its original meaning. An optical device according to one of claims 1 to 22, further comprising at least two different substrates combined together. An optical device according to one of claims 1 to 23, comprising a display device light source (4; 4a ... 4d; 64; 122). The optical device of claim 24, wherein said display device light source is a liquid crystal display (LCD) device (130). ΕΡ 1 485 747 / ΡΤ 5/7 The optical device of claim 25, wherein an angular selective diffuser is located between a light source (122) and the liquid crystal (130) of said LCD. An optical device according to claim 24, wherein said display device light source is an organic light emitting diode (OLED) display device, having an angle of divergence. An optical device according to one of claims 24 to 27, further comprising a microlens array aligned laterally with said display device light source. An optical device according to one of claims 1 to 28, wherein said substrate (20) is partially transparent, to allow for self-viewing operation. An optical device according to any one of claims 1 to 29, further comprising an opaque surface, located on or on said substrate (20), so as to block the entry of light through the substrate from an external scene. An optical device according to one of Claims 1 to 30, further comprising a variable transmittance surface, located so as to attenuate the light input passing through the substrate (20), to control the light brightness passing through the device from an external scene. An optical device according to claim 31, which comprises an automatic device for automatically controlling the transmittance of said variable transmittance surface, whereby the transmittance of the filter is determined by the lightness of the light directed to traverse the substrate (20). The optical device of one of claims 1 to 32, wherein said at least one partial reflection surface (22) reflects the light waves retained in one direction to reach an eye of an observer. ΕΡ 1 485 747 / ΡΤ 6/7 An optical device according to one of claims 1 to 32, wherein said at least one partial reflection surface (22) reflects the waves retained in one direction to reach both eyes of an observer. The optical device of claim 34, further comprising a plurality of display device light sources (4a ... 4d). The optical device of claim 35, wherein the images coming from said plurality of display device light sources (4a ... 4d) differ from each other. An optical device according to any one of claims 1 to 36, wherein said device (16) couples light from the external scene on said substrate (20). An optical device according to one of claims 1 to 37, further comprising a stellar light amplifier (116). Optical device according to one of Claims 33 to 38, in which the device is configured to be arranged on the side of the observer's head, with the lens located behind and the eyepiece at the front. An optical device according to one of claims 1 to 39, wherein said device is mounted on a spectacle frame (100). Optical device according to one of claims 1 to 39, wherein said device is located within a mobile communication device Optical device according to one of claims 1 to 32, wherein said at least one partial reflection surface (22) reflects the light waves retained in a direction to illuminate an object. ΕΡ 1 485 747 / ΡΤ 7/7 The optical device of claim 42, wherein said object is a liquid crystal display device (130). Lisbon,